Many fluids from subterranean formations, such as petroleum feedstocks, contain a large number of components with a very complex composition. For the purposes herein, a formation fluid is the product from an oil well from the time it is produced until it is refined. Some of the potentially fouling-causing components present in a formation fluid, for example wax and asphaltenes, are liquid under ambient conditions, but may aggregate or deposit under lower temperatures and pressures. Additionally, blending feedstocks of different compositions which are incompatible may also make asphaltenes come out of solution and cause problems; in a non-limiting instance such as when heavy Canadian crude oil is blended with shale oil. Waxes comprise predominantly high molecular weight paraffinic hydrocarbons, i.e. alkanes. Asphaltenes are typically dark brown to black-colored amorphous solids with complex structures and relatively high molecular weight and varying degrees of polarity depending on their origin compared to other crude oil components.
In addition to carbon and hydrogen in the composition, asphaltenes also may contain nitrogen, oxygen and sulfur species, as well as metals including, but not necessarily limited to vanadium, nickel, etc. Typical asphaltenes are known to have different solubilities in the formation fluid itself or in certain solvents like carbon disulfide, but are insoluble in solvents like light paraffinics, such as but not including pentane, heptane, etc.
For example, asphaltenes are most commonly defined as that soluble class of materials of crude oil, which is insoluble in heptane or pentane, but which is soluble in xylene and toluene. Asphaltenes exist in the form of colloidal dispersions stabilized by other components in the crude oil or other petroleum feedstock, and they may also exist as soluble species. They are the most polar fraction of crude oil, and often will be subjected to compositional and morphological changes and precipitate upon pressure changes, temperature changes, and indirect factors such as resulting from blending with another, incompatible crude oil, or other mechanical or physicochemical processing. Compositional changes include, but are not necessarily limited to, blending with different fluids such as other hydrocarbon mixtures, water, and other liquids that may adversely affect the solubility of asphaltenes in the resulting mixture.
As will be discussed in further detail, asphaltenes in petroleum feedstocks are known to cause issues like sludge, plugging deposits, fouling and corrosion in production, transferring and processing of the petroleum feedstocks, thereby increasing operating and maintenance costs of production. In one non-limiting embodiment, sludge refers to the residual, semi-solid material left or deposited or precipitated from the petroleum feedstocks.
Asphaltene precipitation occurs in pipelines, separators, valves, furnaces, heat exchangers and other equipment. Once formed and/or deposited, asphaltenes present numerous problems for crude oil producers. For example, asphaltene deposits can partially or completely plug or block downhole tubulars, well-bores, choke off pipes, pipelines, transfer lines or other conduits, valves and/or safety devices, and interfere with the functioning of separator equipment. These phenomena may result in shutdown, loss of production and risk of explosion or unintended release of hydrocarbons into the environment either on-land or off-shore.
In further detail, when the formation fluid from a subsurface formation, such as crude oil, comes into contact with a pipe, a valve, or other production equipment of a wellbore, or when there is a decrease in temperature, pressure, or change of other conditions, asphaltenes may precipitate or separate out of a well stream or the formation fluid while flowing into and through the wellbore to the wellhead. While any asphaltene separation or precipitation is undesirable in and by itself, it is much worse to allow the asphaltene precipitants to accumulate by sticking to the equipment in the wellbore. Any asphaltene precipitants sticking to the wellbore surfaces may narrow pipes; and clog wellbore perforations, various flow valves, and other well site and downhole locations. This may result in well site equipment failures. It may also slow down, reduce or even totally prevent the flow of formation fluid into the wellbore and/or out of the wellhead.
Similarly, undetected precipitations and accumulations of asphaltenes in a pipeline for transferring crude oil could result in loss of oil flow and/or equipment failure. Crude oil storage facilities could have maintenance or capacity problems if asphaltene precipitations occur. These fluids also carry unstable asphaltenes into the refinery, as well as possibly into finished fuels and products where the asphaltenes cause similar problems for facilities of this nature.
In general, when a petroleum feedstock or a hydrocarbon mixture has formed an additional phase with objectionable or problematic properties, the mixture may be characterized as “unstable” or as “demonstrating instability.”
There are large incentives to mitigate fouling in refining. There are large costs associated with shutting down production units because of the fouling components within, as well as the cost to clean the units. Further, the asphaltenes may create an insulating effect within the production unit, and may reduce the efficiency and/or reactivity, and the like. In either case, reducing the amount of fouling-causing components would reduce the cost of hydrocarbon fluids and the products derived therefrom. Additional operational problems in refinery and other processing include, but are not necessarily limited to, fouling of heat exchangers and furnaces, increased tube skin temperatures of furnaces, increased unit upsets, increased pollution, loss of through-put, difficulty with desalting, increased load on wastewater plants, increased in air emissions, and reduced flexibility in plant operations, and the like.
Thus, it would be desirable to develop a method and composition for reducing the amount of fouling-causing components within a petroleum feedstock.